A new approach to the functional systems of the brain

Action is the means by which animals survive. It consists of a complex combination of movements that are either innately endowed or acquired by learning. Innate and learned actions are controlled by different levels of neural networks: innate actions are controlled by reflex mechanisms and pattern generators in the spinal cord and brainstem, whereas learned actions are controlled by the cerebral cortex, basal ganglia, and cerebellum. However, these mechanisms are by no means independent. Recent studies have shown that multiple brain areas contribute to the implementation of learned actions. Based on a series of studies using a sequenced learning task with trial and error, we propose a hypothetical scheme in which a sequential procedure is acquired independently by two cortical systems, one using spatial coordinates, and the other using motor coordinates. They are active preferentially in the early and late stages of learning, respectively. Both of the systems are supported by loop circuits formed with the basal ganglia and the cerebellum, the former for reward-based evaluation and the latter for processing of timing. The proposed neural architecture would operate in a flexible manner to acquire and execute multiple sequential procedures.